JP3915367B2 - Control device for variable valve engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a variable valve engine capable of arbitrarily controlling valve timings (opening and closing timings) of intake valves and exhaust valves.
[0002]
[Prior art]
Conventionally, as shown in JP-A-8-200025, etc., a variable valve device, for example, an electromagnetic drive device, is used to drive an intake valve and an exhaust valve so that the opening / closing operation can be arbitrarily controlled. There is something.
[0003]
In particular, in the variable valve engine described in the above publication, output control is performed by operating the main and sub intake valves and exhaust valves provided two at a time for each cylinder in different combinations according to engine operating conditions by using electromagnetic drive. Like to do.
[0004]
Furthermore, in recent years, for the purpose of improving fuel efficiency by reducing pump loss, the intake valve closing timing is determined according to the target torque (target intake air amount) determined by engine operating conditions, and the intake valve closing timing is controlled. Those that perform non-throttle operation by controlling the amount of intake air are attracting attention and are being developed.
[0005]
[Problems to be solved by the invention]
By the way, in the variable valve engine, the valve timing can be freely set. Therefore, by controlling the valve overlap (at least one of the intake valve opening timing and the exhaust valve closing timing) between the intake valve and the exhaust valve, the internal EGR rate is controlled. The emission (especially NOx emission amount) can be reduced by increasing the internal EGR rate. On the other hand, if the internal EGR rate is excessively increased, combustion becomes unstable, torque fluctuations increase, and drivability deteriorates.
[0006]
Therefore, when non-throttle operation is performed, the internal EGR rate is close to the maximum within the allowable limit range of torque fluctuation on the isotorque line using the intake valve closing timing and the valve overlap of the intake and exhaust valves as parameters. Valve timing (intake valve closing timing and valve overlap) is determined in advance, and the intake valve closing timing and valve overlap are controlled to a predetermined combination in accordance with a target torque determined by engine operating conditions. It was thought that.
[0007]
However, in this way, by controlling the intake valve closing timing and valve overlap to a predetermined combination according to the target torque determined by the engine operating conditions, the engine is always operated near the allowable limit of torque fluctuation. Then, it is conceivable that torque fluctuations exceeding the allowable limit occur due to variations caused by external factors such as engine coolant temperature, intake air temperature, and spark plug contamination.
[0008]
In view of such a situation, the present invention realizes non-throttle operation, while reducing the emission by increasing the internal EGR rate within the allowable range of torque fluctuation regardless of variations in external factors. It is an object of the present invention to provide a control device for a variable valve engine that can be used.
[0009]
[Means for Solving the Problems]
Therefore, in the invention according to claim 1, the valve timings of the intake valve and the exhaust valve (intake valve opening timing, intake valve closing timing , exhaust valve opening timing and exhaust valve closing timing) can be arbitrarily controlled , respectively. In a variable valve engine that controls the amount of intake air by controlling the closing timing, as shown in FIG. 1, target torque calculation means for calculating target torque according to engine operating conditions, and detection of engine torque fluctuation amount A map that gives an isotorque line with parameters of the torque fluctuation amount detecting means, the intake valve closing timing, and the valve overlap of the intake valve and the exhaust valve (at least one of the intake valve opening timing and the exhaust valve closing timing); On the basis of the target torque, a corresponding equal torque line is selected from the map, and on the selected equal torque line, the torque fluctuation amount is allowed according to the torque fluctuation amount. With an internal EGR rate within a range of the field to select a valve overlap to be near the maximum, at equal torque line said selected intake valve closing for realizing the target torque corresponding to the selected valve overlap Valve timing control means for selecting a timing and controlling the selected intake valve closing timing in combination with a valve overlap is provided.
[0010]
In the invention according to claim 2, the valve timing control means selects a valve overlap in the direction of increasing the internal EGR rate when the torque fluctuation amount is smaller than the allowable limit value on the equal torque line, and the torque fluctuation amount is When the value is larger than the allowable limit value, the valve overlap in the direction of decreasing the internal EGR rate is selected .
[0011]
The invention according to claim 3 is characterized in that the valve timing control means controls the overlap position with a constant overlap amount as a valve overlap.
[0012]
The invention according to claim 4 is characterized in that the valve timing control means controls the intake valve opening timing while keeping the exhaust valve closing timing constant as valve overlap.
[0013]
The invention according to claim 5 is characterized in that the valve timing control means controls the exhaust valve closing timing while keeping the intake valve opening timing constant as valve overlap.
[0014]
The invention according to claim 6 is characterized in that the torque fluctuation amount detecting means detects the torque fluctuation amount from the fluctuation amount of the engine speed.
The invention according to claim 7 is characterized in that the torque fluctuation amount detecting means detects the torque fluctuation amount from the fluctuation amount of the in-cylinder pressure of the engine.
[0015]
【The invention's effect】
According to the first aspect of the present invention, according to the torque fluctuation amount actually detected on the isotorque line having the intake valve closing timing and the valve overlap as parameters with respect to the target torque determined by the engine operating condition. In addition, non-throttle operation can be realized by controlling the combination of the intake valve closing timing and valve overlap so that the internal EGR rate is near the maximum within the allowable range of torque fluctuation, while the engine cooling water temperature and intake air temperature are Furthermore, regardless of variations due to external factors such as spark plug fouling, the engine can always be operated within the allowable range of torque fluctuations, and the internal EGR rate can be maximized to reduce NOx. According to the invention of claim 2, when the torque fluctuation amount is smaller than the allowable limit value on the equal torque line, the valve timing is increased in the direction of increasing the internal EGR rate. Controls, when the amount of torque fluctuation is larger than the allowable limit value, by controlling the valve timing in the internal EGR rate decreasing direction, with respect to changes in the external factors can be controlled to quickly optimum combination.
[0016]
According to the invention of claim 3, as the valve overlap, by controlling the overlap position with a constant overlap amount, the internal EGR rate is increased and delayed by increasing the overlap position. Thus, the internal EGR rate can be reduced.
[0017]
According to the invention of claim 4, as the valve overlap, the exhaust valve closing timing is made constant and the intake valve opening timing is controlled to increase the internal EGR rate by increasing the intake valve opening timing, The internal EGR rate can be reduced by delaying the intake valve opening timing.
[0018]
According to the invention according to claim 5, as the valve overlap, by controlling the exhaust valve closing timing while keeping the intake valve opening timing constant, the internal EGR rate is increased by increasing the exhaust valve closing timing, The internal EGR rate can be decreased by delaying the exhaust valve closing timing.
[0019]
According to the invention of claim 6, the torque fluctuation amount can be detected from the fluctuation amount of the engine speed without providing a special sensor.
According to the seventh aspect of the present invention, the in-cylinder pressure sensor is required, but the torque fluctuation amount can be detected with high accuracy from the fluctuation amount of the engine in-cylinder pressure.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 2 is a system diagram of a variable valve engine showing an embodiment of the present invention.
[0021]
The combustion chamber 3 defined by the piston 2 of each cylinder of the engine 1 is provided with an electromagnetically driven intake valve 5 and an exhaust valve 6 so as to surround the spark plug 4. 7 is an intake passage and 8 is an exhaust passage.
[0022]
FIG. 3 shows the basic structure of an electromagnetic drive device (variable valve operating device) for the intake valve 5 and the exhaust valve 6. A plate-like movable element 22 is attached to the valve shaft 21 of the valve body 20, and the movable element 22 is biased to a neutral position by springs 23 and 24. A valve opening electromagnetic coil 25 is disposed below the mover 22, and a valve closing electromagnetic coil 26 is disposed above the movable element 22.
[0023]
Therefore, when opening the valve, after energization of the upper valve closing electromagnetic coil 26 is stopped, by energizing the lower valve opening electromagnetic coil 25 and attracting the mover 22 downward, The valve body 20 is lifted and opened. Conversely, when closing the valve, by energizing the lower valve opening electromagnetic coil 25 and then energizing the upper valve closing electromagnetic coil 26 to attract the mover 22 upward, The valve body 20 is seated on the seat portion and closed.
[0024]
Returning to FIG. 2, an electric throttle valve 9 is provided in the intake passage 7 upstream of the intake manifold.
The intake passage 7 is also provided with an electromagnetic fuel injection valve 10 for each cylinder in each branch portion of the intake manifold.
[0025]
Here, the operation of the intake valve 5, the exhaust valve 6, the electric throttle valve 9, the fuel injection valve 10 and the spark plug 4 is controlled by the control unit 11, and the control unit 11 has a crank in synchronization with the engine rotation. A crank angle sensor 12 that outputs an angle signal and can detect the engine speed Ne together with the crank angle position, an accelerator pedal sensor that detects an accelerator opening (accelerator pedal depression amount) APO (an idle switch that is turned on when the accelerator is fully closed) 13), an air flow meter 14 for detecting the intake air amount Qa upstream of the throttle valve 9 in the intake passage 7, a water temperature sensor 15 for detecting the engine cooling water temperature Tw, and an ignition plug 4 for detecting the in-cylinder pressure Pc if necessary. A signal is input from a piezoelectric in-cylinder pressure sensor 16 or the like provided as a washer.
[0026]
In this engine 1, for the purpose of improving fuel efficiency by reducing pump loss, the opening / closing operation of the electromagnetically driven intake valve 5 and exhaust valve 6 is controlled, and in particular, the intake valve 5 is controlled by variably controlling the closing timing IVC of the intake valve 5. Control and perform substantially non-throttle operation. In this case, the electric throttle valve 9 is provided downstream of the throttle valve 9 in the intake passage 7 (inside the intake manifold) for the purpose of obtaining a negative pressure required for canister purge, crankcase purge, and the like.
[0027]
The fuel injection timing and the fuel injection amount of the fuel injection valve 10 are controlled based on the engine operating conditions. The fuel injection amount is basically determined based on the intake air amount Qa detected by the air flow meter 14. It controls so that it may become the air fuel ratio.
[0028]
The ignition timing by the spark plug 4 is controlled to MBT (optimum ignition timing on torque) or a knock limit based on engine operating conditions.
Next, valve timing control of the intake valve 5 and the exhaust valve 6 will be described in more detail with reference to FIGS. 4 to 6 (first embodiment).
[0029]
FIGS. 4A and 4B are examples in which the internal EGR rate is varied depending on the valve timing setting when a certain target torque is requested. 4 and FIGS. 7 and 10, which will be described later, show the exhaust valve opening timing EVO, the intake valve opening timing IVO, the exhaust valve closing timing EVC, the intake valve in the clockwise direction with reference to the top dead center TDC and the bottom dead center BDC. The closing timing IVC is shown.
[0030]
In the setting of FIG. 4A, the overlap position is relatively delayed with respect to the valve overlap (intake valve opening timing IVO to exhaust valve closing timing EVC) between the intake valve and the exhaust valve before the top dead center TDC. Therefore, the internal EGR rate is small.
[0031]
On the other hand, in the setting shown in FIG. 4B, both the intake valve opening timing IVO and the exhaust valve closing timing EVC are advanced so that the overlap amount (crank angle between IVO and EVC) remains constant. Since the intermediate crank angle position between IVO and EVC is increased, for example, the internal EGR rate increases. In addition, the intake valve closing timing IVC is delayed in order to obtain equal torque as the internal EGR (residual gas amount) increases. If the internal EGR rate increases with such a setting, the emission (NOx emission amount) is reduced, but the combustion stability tends to deteriorate.
[0032]
FIG. 5 shows an equal torque line, a torque fluctuation allowable limit line, an equal NOx, etc., with the overlap amount (O / L amount) being constant and the intake valve closing timing IVC and the overlap position (O / L position) as parameters. It is the map which showed the line.
[0033]
In order to achieve a certain target torque, there are many combinations of intake valve closing timing IVC and overlap position on the equal torque line, but the earlier the overlap position, the higher the internal EGR rate and the emission (NOx emission amount) is reduced, but combustion stability is deteriorated and torque fluctuation amount is increased.
[0034]
Therefore, for a certain target torque, the valve timing at which the internal EGR rate is near the maximum within the range of the allowable torque fluctuation on the constant torque line, that is, the intersection of the constant torque line and the allowable torque fluctuation limit line (in the figure). It is desirable to control the intake valve closing timing IVC and the overlap position at ().
[0035]
However, because there is a risk that the torque fluctuation allowable limit may be exceeded due to variations in external factors, actual torque fluctuation is detected and valve timing is controlled.
FIG. 6 is a flowchart of the valve timing control, which will be described below.
[0036]
In step 1 (denoted as S1 in the figure, the same applies hereinafter), the accelerator opening APO and the engine speed Ne are read.
In step 2, a target torque (target intake air amount) TQ is calculated from the accelerator opening APO and the engine speed Ne with reference to a map. This portion corresponds to target torque calculation means.
[0037]
However, during idle operation (idle switch ON), based on the deviation ΔNe = Ne−Nidle between the engine speed Ne and the target idle speed Nidle, when the deviation is on the negative side, the increase direction, the positive side In this case, the target torque (target intake air amount) TQ is corrected in the decreasing direction.
[0038]
In step 3, based on the target torque (target intake air amount) TQ, a corresponding isotorque line is selected with reference to the map of FIG.
In step 4, the engine torque fluctuation amount ΔT is detected. This portion corresponds to torque fluctuation amount detection means.
[0039]
Specifically, the engine speed Ne is detected under steady operating conditions, and the variation with respect to the average value, specifically, the standard deviation (or its square value) is calculated based on the time series data of the engine speed Ne. By calculating, the amount of fluctuation of the engine speed Ne is calculated, and this is set as the torque fluctuation amount ΔT.
[0040]
Alternatively, the indicated mean effective pressure Pi is calculated based on the integrated value (area value) of the in-cylinder pressure Pc detected by the in-cylinder pressure sensor 16 in a predetermined crank angle period of the explosion stroke of each cylinder under steady operation conditions. Based on the time series data of the indicated mean effective pressure Pi, a variation with respect to the average value, specifically, a standard deviation (or a square value thereof) is obtained to calculate a fluctuation amount of the indicated mean effective pressure Pi, This is the torque fluctuation amount ΔT.
[0041]
In step 5, the torque fluctuation amount ΔT is compared with a torque fluctuation allowable limit value (torque fluctuation allowable limit value determined in advance according to the target torque TQ) on the equal torque line.
As a result of the comparison, if torque fluctuation amount ΔT ≧ allowable limit value, the routine proceeds to step 6 where the counter C is incremented by 1 (C = C + 1). Conversely, if the torque fluctuation amount ΔT <allowable limit value, the routine proceeds to step 7 where the counter C is decremented by 1 (C = C−1).
[0042]
In Step 8, an overlap position (O / L position) that is C minutes later than the torque fluctuation allowable limit is selected on the equal torque line, and the intake valve opening timing IVO and the exhaust valve closing timing EVC are determined based on this. (Overlap amount is constant).
[0043]
In this case, if the counter C is a negative value, an overlap position that is earlier by −C than the allowable torque fluctuation limit is selected on the equal torque line.
Therefore, when the torque fluctuation amount is larger than the allowable limit value and the counter C is in the increasing direction, control is performed so that the overlap position is delayed (internal EGR decreasing direction) on the equal torque line, and the torque fluctuation amount is within the allowable limit value. When the value is smaller than the value and the counter C is in the decreasing direction, the control is performed in the direction of increasing the overlap position (internal EGR increasing direction) on the equal torque line.
[0044]
In step 9, the intake valve closing timing IVC corresponding to the overlap position (O / L position) is selected on the equal torque line, thereby determining the intake valve closing timing IVC.
In step 10, the valve timings of the intake valve 5 and the exhaust valve 6 are controlled based on the intake valve opening timing IVO, the exhaust valve closing timing EVO, and the intake valve closing timing IVC determined in steps 8 and 9. Here, the steps 3 to 5-9 correspond to the valve timing control means. The exhaust valve opening timing EVO may be constant.
[0045]
Next, a second embodiment will be described with reference to FIGS.
In the second embodiment, as the valve overlap, the intake valve opening timing IVO is controlled by making the exhaust valve closing timing EVC constant.
[0046]
7A, the intake valve opening timing IVO is relatively delayed with respect to the valve overlap (intake valve opening timing IVO to exhaust valve closing timing EVC) between the intake valve and the exhaust valve before the top dead center TDC. Therefore, the internal EGR rate is small.
[0047]
On the other hand, in the setting shown in FIG. 7B, the exhaust valve closing timing EVC is made constant and the intake valve opening timing IVO is advanced (large overlap amount), so the internal EGR rate becomes large. This is because if the intake valve opens quickly before TDC, the exhaust gas in the cylinder blows back toward the intake side, which is sucked in the next stroke. In addition, the intake valve closing timing IVC is delayed in order to obtain equal torque as the internal EGR (residual gas amount) increases. If the internal EGR rate increases with such a setting, the emission (NOx emission amount) is reduced, but the combustion stability tends to deteriorate.
[0048]
FIG. 8 shows an equal torque line, a torque fluctuation allowable limit line, and an equal NOx line with the exhaust valve closing timing EVC constant and the intake valve closing timing IVC and the intake valve opening timing IVO (O / L amount) as parameters. It is the map shown.
[0049]
To achieve a certain target torque, there are many combinations of the intake valve closing timing IVC and the intake valve opening timing IVO on the isotorque line. However, the earlier the intake valve opening timing IVO, the larger the overlap amount. Thus, the internal EGR rate is increased and the emission (NOx emission amount) is reduced, but the combustion stability is deteriorated and the torque fluctuation amount is increased.
[0050]
Therefore, the actual torque fluctuation amount is detected, and the valve timing at which the internal EGR rate is near the maximum within the range of the torque fluctuation allowable limit on the equal torque line with respect to the target torque, that is, the intake valve closing timing IVC and the intake valve Control in combination with the opening time IVO.
[0051]
FIG. 9 is a flowchart of valve timing control in this case. In addition to using the map of FIG. 8 instead of the map of FIG. 5, only the steps 8 and 9 are different from the flow of FIG. explain.
[0052]
In step 8, an intake valve opening timing IVO that is C minutes later than the torque fluctuation allowable limit is selected on the equal torque line, and thereby the intake valve opening timing IVO is determined. The exhaust valve closing timing EVC is constant.
[0053]
In this case, if the counter C is a negative value, the intake valve opening timing IVO that is -C earlier than the torque fluctuation allowable limit is selected on the equal torque line.
Therefore, when the torque fluctuation amount is larger than the allowable limit value and the counter C is increasing, the intake valve opening timing IVO is controlled to be delayed (internal EGR decreasing direction) on the equal torque line, and the torque fluctuation amount is When the counter C is smaller than the allowable limit value and the counter C is decreasing, the intake valve opening timing IVO is controlled earlier (internal EGR increasing direction) on the equal torque line.
[0054]
In step 9, an intake valve closing timing IVC corresponding to the intake valve opening timing IVO is selected on the equal torque line, and thereby the intake valve closing timing IVC is determined.
Next, a third embodiment will be described with reference to FIGS.
[0055]
In the third embodiment, as the valve overlap, the intake valve opening timing IVO is made constant and the exhaust valve closing timing EVC is controlled.
In the setting of FIG. 10A, the exhaust valve closing timing EVC is relatively delayed with respect to the valve overlap (intake valve opening timing IVO to exhaust valve closing timing EVC) between the intake valve and the exhaust valve before the top dead center TDC. Therefore, the internal EGR rate is small.
[0056]
On the other hand, in the setting of FIG. 10B, the intake valve opening timing IVO is kept constant and the exhaust valve closing timing EVC is advanced, so that the internal EGR rate increases. This is because if the exhaust valve closes quickly before the TDC, the exhaust gas in the cylinder does not come out to the exhaust side, but is exhausted to the intake side and sucked in the next stroke. In addition, the intake valve closing timing IVC is delayed in order to obtain equal torque as the internal EGR (residual gas amount) increases. If the internal EGR rate increases with such a setting, the emission (NOx emission amount) is reduced, but the combustion stability tends to deteriorate.
[0057]
FIG. 11 is a map showing an equal torque line, an allowable torque fluctuation limit line, and an equal NOx line with the intake valve opening timing IVO being constant and the intake valve closing timing IVC and the exhaust valve closing timing EVC as parameters.
[0058]
In order to achieve a certain target torque, there are many combinations of intake valve closing timing IVC and exhaust valve closing timing EVC on the equal torque line, but the internal EGR rate increases as the exhaust valve closing timing EVC becomes earlier. Thus, the emission (NOx emission amount) is reduced, but the combustion stability is deteriorated and the torque fluctuation amount is increased.
[0059]
Therefore, the actual torque fluctuation amount is detected, and the valve timing at which the internal EGR rate is near the maximum within the range of the torque fluctuation allowable limit on the equal torque line with respect to the target torque, that is, the intake valve closing timing IVC and the exhaust valve Control is performed in combination with the closing timing EVC.
[0060]
FIG. 12 is a flowchart of the valve timing control in this case. Only the steps 8 and 9 are used with respect to the point that the map of FIG. 11 is used instead of the map of FIG. 5 or FIG. 8 and the flow of FIG. Since this is different, this part will be described.
[0061]
In step 8, an exhaust valve closing timing EVC that is C minutes later than the torque fluctuation allowable limit is selected on the equal torque line, thereby determining the exhaust valve closing timing EVC. The intake valve opening timing IVO is constant.
[0062]
In this case, if the counter C is a negative value, the exhaust valve closing timing EVC that is earlier by −C than the allowable torque fluctuation limit on the equal torque line is selected.
Therefore, when the torque fluctuation amount is larger than the allowable limit value and the counter C is increasing, the exhaust valve closing timing EVC is controlled to be delayed (internal EGR decreasing direction) on the isotorque line. When the counter C is smaller than the allowable limit value and the counter C is decreasing, the exhaust valve closing timing EVC is controlled to be advanced earlier (internal EGR increasing direction) on the equal torque line.
[0063]
In step 9, an intake valve closing timing IVC corresponding to the exhaust valve closing timing EVC is selected on the equal torque line, and thereby the intake valve closing timing IVC is determined.
In any of the first to third embodiments described above, non-throttle operation can be realized, but torque fluctuations are always maintained regardless of variations caused by external factors such as engine cooling water temperature, intake air temperature, and spark plug contamination. It is possible to operate within the allowable limits, and to maximize the internal EGR rate to reduce NOx. [Brief description of the drawings]
1 is a functional block diagram showing the configuration of the present invention. FIG. 2 is a system diagram of a variable valve engine showing an embodiment of the present invention. FIG. 3 is a basic structural diagram of an electromagnetic drive device for intake and exhaust valves. FIG. 5 is a diagram showing an example of valve timing of the first embodiment. FIG. 5 is a diagram showing an equal torque map of the first embodiment. FIG. 6 is a flowchart of valve timing control of the first embodiment. FIG. 8 is a view showing an equal torque map of the second embodiment. FIG. 9 is a flow chart of valve timing control of the second embodiment. FIG. 10 is a view showing an example of valve timing of the third embodiment. FIG. 11 is a diagram showing an equal torque map of the third embodiment. FIG. 12 is a flowchart of valve timing control of the third embodiment.
1 Engine 4 Spark plug 5 Electromagnetically driven intake valve 6 Electromagnetically driven exhaust valve 7 Intake passage 8 Exhaust passage 9 Fuel injection valve 10 Electric throttle valve 11 Control unit 12 Crank angle sensor 13 Accelerator pedal sensor 16 In-cylinder pressure sensor

Claims (7)

In a variable valve engine that can arbitrarily control the intake valve opening timing, intake valve closing timing, exhaust valve opening timing and exhaust valve closing timing, and controlling the intake air amount by controlling the intake valve closing timing ,
Target torque calculating means for calculating a target torque according to engine operating conditions;
Torque fluctuation amount detecting means for detecting the torque fluctuation amount of the engine;
A map that gives an isotorque line with the intake valve closing timing and the valve overlap of the intake and exhaust valves as parameters,
On the basis of the target torque, a corresponding equal torque line is selected from the map, and the internal EGR rate is within the allowable limit range of the torque fluctuation amount according to the torque fluctuation amount on the selected equal torque line. A valve overlap that is close to the maximum is selected, and an intake valve closing timing that realizes the target torque corresponding to the selected valve overlap is selected on the selected equal torque line, and the selected intake air Valve timing control means for controlling a combination of valve closing timing and valve overlap;
A control apparatus for a variable valve engine, comprising: The valve timing control means selects a valve overlap in the direction of increasing the internal EGR rate when the torque fluctuation amount is smaller than the allowable limit value on the isotorque line, and when the torque fluctuation amount is larger than the allowable limit value, 2. The control device for a variable valve engine according to claim 1 , wherein the valve overlap in the direction of decreasing the internal EGR rate is selected .   3. The control apparatus for a variable valve engine according to claim 1, wherein the valve timing control means controls the overlap position with a constant overlap amount as valve overlap.   3. The control apparatus for a variable valve engine according to claim 1, wherein the valve timing control means controls the intake valve opening timing while keeping the exhaust valve closing timing constant as valve overlap.   The variable valve engine control apparatus according to claim 1 or 2, wherein the valve timing control means controls the exhaust valve closing timing while keeping the intake valve opening timing constant as valve overlap.   6. The control apparatus for a variable valve engine according to claim 1, wherein the torque fluctuation amount detection means detects a torque fluctuation amount from a fluctuation amount of the engine speed.   6. The control apparatus for a variable valve engine according to claim 1, wherein the torque fluctuation amount detection means detects a torque fluctuation amount from a fluctuation amount of an in-cylinder pressure of the engine.

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